The invention relates to a semiconductor diode such as is disclosed in the preamble of patent claim 1.
It is known that in the case of pn-diodes as well as in the case of Schottky-diodes, the threshold voltage essentially is determined by the band width of the utilized semiconductor. For small threshold voltages, semiconductors with a minimal band width are generally required. The fabrication of narrow band semiconductor-diodes, however, is at the present time still very difficult and costly.
Furthermore, it is known that, in the case of pn-diodes, minority carrier effects dominate, and in the case of Schottky-diodes, majority carrier effects dominate. Accordingly, Schottky-diodes have substantially higher cut-off frequencies than pn-diodes.
From "Solid State Electronics" (1976), Vol. 19, Pages 625-631, a so-called barite-pn-diode is known which is utilized as a generator for producing very high frequencies; for example, 10 GHz. In this diode, transit time effects are utilized which essentially occur in the central intermediate layer of the diode. This intermediate layer, as is shown in FIG. 1 of this publication, manifests a construction and a doping in which, without an applied external voltage, aside from the most extreme marginal regions, there is virtually no depletion of free charge carriers. The high field strengths in this intermediate layer, necessary in order to utilize the transit time effects, require that this intermediate layer manifest a considerable minimum doping. The thickness of this intermediate layer, conditioned in turn by the specified frequency to be generated, leads to the result that only the previously mentioned marginal regions are depleted of free charge carriers.
Likewise serving the production of high frequency is an impact avalanche transit-time diode known from the German Offenlegungschrift No. 2,224,159 which is constructed of two p- and n-semiconductor layers superimposed on a metal electrode. The central layer, in the case of this hetero-construction, is to manifest a doping in comparison with the above-disposed semiconductor layer which is approximately greater by two orders of magnitude, so that, when operating voltage is lacking, even in the case of such a diode, virtually only marginal regions of this central layer manifest a depletion of free charge carriers, such as is, moreover, known of every pn-junction.